1. Field of the Invention
This invention is related to skis, snowboards and the like and, more particularly, an improved ski design, as well as an improved, more versatile and efficient method for making skis.
2. Description of the Prior Art
Current designs for skis, snowboards and similar products, particularly Alpine snow skis, require a batch (non-continuous) manufacturing process. Performance criteria for skis have led to a general practice whereby each ski has only one axis of geometric symmetry (for example, symmetry along the longitudinal axis of the ski). The properties required for acceptable ski performance have dictated the parameters of conventional ski design and have determined how a ski can be manufactured.
For instance, a ski must distribute the skier's weight along its length. Therefore, a lengthwise curvature or "camber" is conventionally built into the skis such that applied body weight flattens the ski and ensures that a moderate pressure load is applied at the tip of the ski and the tail of the ski, in the downward direction normal to the surface on which the ski is placed.
Proper ski performance also requires that the ski conventionally be provided with a "side cut". This simply means that the ski must have a change in width along its length, for example, being wider in the tip or shovel area than in the central or waist area, where the boot is placed. The ski may also be wider in the tail than in the central waist area. With a side cut, the ski will contact the surface at only its widest parts when the ski is placed on edge, until additional load is applied at the boot attachment area, whereupon a radius of curvature is achieved. This is what takes place when one is "carving a turn".
Another design factor is that maximum bending moments, and hence stresses, are achieved when uneven terrain causes the skier to be supported at only the ends of the ski. This has previously been accommodated by increasing the thickness of the ski progressively from each end towards a maximum thickness in the middle of the ski. Material selection and fiber angles (in the case of composite construction) can also play a role in compensating for these high-stress conditions.
Hard skiing surfaces sometimes initiate unwanted vibrations. These vibrations are currently diminished by high-loss materials distributed about the construction of the ski. "High-loss materials" are materials which dissipate a portion of the vibration energy viscously such that the small amount of heat generated damps out the vibration.
In the case where the ski is expected to perform by making very rapid turns, lateral moments of inertia on the ski, known as "swingweights", must be minimized. This is currently aided by reducing the thickness of the ski away from the middle region and by the use of low-density materials, including composites.
It is desirable for skis to follow the terrain as closely as possible, thus requiring a relatively small lengthwise bending rigidity. The degree of bending rigidity which a ski possesses is sometimes discussed in terms of "flex". The greater the flex in the ski, the smaller the lengthwise bending rigidity. When fully loaded, almost the entire length of the ski or snowboard contributes to carving a turn. However, predominant rudder effect is exerted by the tip of the ski or snowboard. This requires a relatively large torsional rigidity, i.e, a higher resistance to twisting, such that rotation of the ski about its longitudinal axis is equivalent at the boot, the tip and the tail when initiating a turn, so that the ski nearly approximates a rigid body. If a ski is too soft in torsional rigidity, then a turn initiating lateral rotation of the ski at the boot will result in a smaller rotation at the tip. Hence, torsional softness results in much larger turn radii for a given side cut, when the ski is turned on edge. The result is a ski which makes "sluggish" turns.
If the ski has an insufficient load at its tip or if vibrations cause the tip to lose contact with the surface, then inadequate ski turn control is experienced. A small initial camber (0.2"-0.75", for example) assists in providing some lengthwise load distribution, and hence tip load (1-lb. to 6-lb., for example) upon flattening the ski.
Prevailing advice using current ski designs and manufacturing processes would have high-speed skiers use relatively higher bending rigidities (less flex) and vice versa. This allows for more accurate and responsive turning, at the expense of the ski's ability to follow the terrain, given that higher torsional rigidity always follows higher lengthwise bending rigidity, using conventional ski designs. The height and weight of skiers has traditionally dictated the length of the ski required, for all of the reasons described above.
Given the multitude of different lengths, side cuts, camber and torsional rigidities required, batch manufacturing of Alpine skis, cross-country skis, snowboards and the like, using closed molds or similar methods, is unreasonably expensive. It is therefore an object of the present invention, contrary to conventional designs and methods, to provide a device and method whereby lengthwise bending rigidities can be reduced (i.e., increased flex), and torsional rigidities can be increased simultaneously by non-conventional continuous ski manufacturing methods and designs. It is a further object to provide numerous intermediate step changes in the torsional stiffness of the device, so that any ski length can be provided, by a continuous manufacturing process which utilizes a single tooling cavity to form the ski. A different set of tooling for each size ski is not required. It is a still further object to provide a device and method whereby increased tip and tail loads, and hence load distribution and turn control, may be easily achieved with skis having a much lower lengthwise bending rigidity, contrary to conventional ski designs.
Others have sought to depart from conventional ski designs and manufacturing methods. U.S. Pat. No. 5,299,822 to Mayr et al. discloses a shell ski formed by a plurality of U sections connected to a plate-shaped part with connecting sections. The adjacent U sections form hollow spaces. A cover plate is secured to the top of the ski. A front shovel and a tail having lugs are attached to the ski by inserting the lugs into the ski body. The U sections may be formed by pultrusion.
U.S. Pat. No. 5,249,819 to Mayr discloses a ski having a hollow ski body. The ski body may have the same width over the entire length of the ski, and it is possible to use a core of extruded profiles which are continuously produced and cut to the length of the ski.
U.S. Pat. No. 3,933,362 to Sakuma et al. and U.S. Pat. No. 3,940,157 to Sakuma disclose ski structures having a hollow core. U.S. Pat. No. 5,265,911 to Goode discloses a pultruded, hollow ski pole. The pole may be comprised of different layers having fibers arranged in a crisscross or dual opposed lattice to provide greater strength. U.S. Pat. No. 5,294,151 to Goode discloses another hollow pultruded ski pole.
Finally, U.S. Pat. No. 5,366,773 to Schroll et al. discloses a method of making pultruded members. One example of these pultruded members has a rectilinear cross section.
None of the patents identified above discloses the specific design or manufacturing method for producing a hollow ski by a continuous manufacturing process, which method or design produces all of the advantages set forth in the objects discussed above.